He established a price target of $50 for Twitter shares before its IPO, which carried a price of $26 per share. He lowered his rating to hold two weeks ago when the stock hit $59. It traded at $60.60 Monday morning, falling another 5 percent after Friday's 13 percent plunge.

Twitter's market value equals one-third that of its more established rival Facebook, even as Facebook has five times more users and 10 times more revenue, The Time reports.

"You're starting to hear it: 'it's a new world order.' Apparently the sun is going to rise in the west because of Twitter," Timothy Connolly, a New York City money manager, tells the paper. "It's absolutely beyond ridiculous."

"At the end of the day, we have thought and we continue to think the valuation is just initially stretched," he tells CNBC. "It's excessive. It appears now that we've approached some kind of mania. When that happens, you just kind of have to wait and see what happens."